When milling and drilling of fiber-reinforced materials such as CFRP, GFRP and polyester filament-reinforced plastics, the problem that occurs often is a tearing of individual fibers or polyester yarns are fanning out, when a workpiece of such a material is machined with conventional tools for machining. Thus, individual fibers are torn from the edge of the machined area and others are pressed during passage of the tool to the edge of the machined area, so that they are cut only on an end protruding over the edge of the machined area and therefore protrude over the rim after machining. Usually, therefore, a post machining, ie a finishing or reaming is performed after a rough machining or roughing.
Starting from finishing-roughing-cutters known in metalworking, such as described in German patent DE 3742942 C1 or German utility model DE 8609688 U1 or U.S. Pat. No. 4,285,618 B, wherein each roughing cutting edge is associated with a trailing finishing cutting edge, also in the machining of fiber-reinforced materials and of sandwich materials with such materials efforts have been made with the aim of being able to accomplish both a rough machining, ie a roughing workstep, as well as a postmachining, ie a postreaming or finishing workstep with a single tool, in order to arrive at an improved surface quality with less processing time.
For example, German utility model DE 202 09 768 U shows a step drill for machining sandwich materials, wherein the main cutting edges at the step are offset to one another so that the one main cutting edge premachines and the other postreams. German utility model DE 202 11 589 U1 shows another drill for machining sandwich workpieces, wherein two premachining lands are more or less blunt designed as broaching tools and the postmachining lands trailing in the circumferential direction with sharp minor cutting edges as reamers. Similar drills are shown in the utility models DE 202 11 592 U and DE 203 04 580 U1, wherein there, broad circular grinding chamfers are used for reinforcement of the drilled hole and rounded cutting corners in order to prevent tearing of the thread.
An end milling cutter for machining of fiber reinforced plastics, wherein the idea of a separation of functions in the main cutting work doing, leading machining lands and only postmachining, trailing lands has also been implemented, is shown in German Patent DE 112 009 000 013 B4. There, the leading lands have a left-hand twist and the trailing lands have a right-hand twist. There, this is to avoid burrs.
Furthermore, milling tools are known from the machining of plastics, which are, similar to files, on the peripheral surfaces of their machining lands, provided with teeth, particularly generated by intersecting grooves with a depth which is relative to the tool diameter relatively small. Such a tool is already shown in German patent DE 736 449, and in German patent DE 10232037 B4 of the applicant.
The use of tools with shell grooves and chip breaker grooves for the processing of fiber-reinforced materials is disclosed in U.S. Pat. No. 5,221,163 and in international application WO 2010/061933 A1.
U.S. Pat. No. 6,164,876 discloses a tool with two lands, one of which has a plurality of teeth and the other a conventional cutting edge.